Twistless multifilament yarn of polyethylene terephthalate



NOV. 5, 1968 1, F MclNTYRE ETAL 3,409,496

TWISTLESS MULTIFILAMENT YARN OF FOLYETHYLENE TEREPHTHALATE original Filed Nov. 15, 1963 Arve/vaya Unted States Patent O s Claims. (l. 161-179) This invention relates to coherent multifilament yarn made from hydrophobic synthetic thermoplastic polymers.

This is a division of our copending application Ser. No. 324,091, filed Nov. 15, 1963. i

During the processing of multifilament yarns including various winding operations, and in use when making fabrics e.g. by weaving or knitting, it is desirable that the yarn should exhibit a certain amount of cohesion in order to prevent individual filaments becoming separated from the others and thereby causing snagging and breakage. For this reason multifilament yarns are usually provided with a degree of cohesion by twisting or sizing processes or by a combination of such processes. Twisting provides a physical restraint to separation of single filaments, whereas sizing provides a polymeric binding agent or adhesive to hold the filaments together. Such processes tend to be slow and expensive. Moreover sizing processes as at present known are less satisfactory for hydrophobic yarns, such as polyester yarns and yarns from polymerised olefines, than for more hydrophilic yarns such as those derived from the natural fibres, regenerated cellulose fibres, and wholly synthetic fibres, such as the commercially available polyamides, which are relatively hydrophilic due to the presence of hydrogen bonding units in the chemical structure. Another method of providing a degree of cohesion which has been suggested consists in passing the filaments through a tube in a high velocity air stream, whereby an electrostatic charge is generated and physical cohesion is obtained by intermingling or interlacing of the single filaments. Yet another method which has been suggested for obtaining cohesion for yarns of thermoplastic synthetic linear polymers consists in wetting the multifilaments with water and then heating them above 100 C. while applying external mechanical force. This process can be Satisfactory for less hydrophobic polymers such as polyamides, but when applied to fibres derived from very hydrophobic materials such as polyesters or polymerised olefines it is unsatisfactory because the pressure required to obtain interfilament cohesion is such that the shape of the yarn and of individual filaments composing the yarn, is drastically altered.

In some end-uses, such as for sewing threads, it is desirable that the multifilament yarn should exhibit a very high degree of cohesion, sometimes even to the extent that complete inter-filament cohesion is required. In other end-uses, such as for weaving, it is desirable that the degree of cohesion should be such as to prevent separation of individual filaments during processing but later, that a physical or chemical treatment of the final product, such as rapid flexing or scouring, should reduce the degree of cohesion or even disjoin the individual filaments.

The cohered multifilament yarn becomes stiffer than the untreated uncohered yarn. For a sewing thread it is usual to make the yarn as flexible as possible, e.g. by inserting twist; it is therefore surprising that our cohered multifilament is eminently suitable as a sewing thread.

According to our invention we provide a coherent thermoplastic substantially twistless multifilament yarn Fice made from a hydrophobic synthetic thermoplastic polymer possessing in the form of oriented fibres a Water absorbency of less than 1% at 70 F. and 65% relative humidity, wherein each filament adheres to adjacent filaments by bonds extending substantially for the whole length of the filaments each bond varying in strength along its length, said bond consisting of the hydrophobic synthetic thermoplastic polymer of which the filaments are composed so that any cohered portion between and including the filaments consists of a chemically continuous phase of the same polymer further characterised in that said bond consists of the polymer in a crystalline or partly crystalline form, the degree of cohesion being defined by an average cohered filament count of 5-80% of the total number of filaments in the untreated and uncohered yarn.

The degree of cohesion at any point along the length of the yarn is substantially the same, although the individual filaments cohered may not be the same.

On partial breakdown of cohesion brought about by light abrasion over a guide or peg such that at least two filament bundles but not more than 6 filament bundles (where a filament bundle can be any number of filaments from l to n-l where n is the number of filaments in the multifilament yarn) are produced, then the length of the bundle which is detached is not more than 20 cms.

We also provide a process for the production of a coherent multifilament yarn from a hydrophobic synthetic thermoplastic polymer comprising wetting the surface of the filaments of a multifilament yarn with a liquid which contains a compound which is a solvent for the oriented filaments at an elevated temperature, then passing the filaments under a controlled tension through a heating zone at a temperature and for a time such that the individual filaments cohere to one another and the solvent is evaporated from the surface of the yarn until the polymer forms a continuous phase from at least one filament through any cohered portion to another adjoining filament. The solvent should be applied when the yarn is under controlled tension which is maintained Whilst the solvent is evaporated preferably by heating and before windup.

The process is remarkably versatile and widely differing degrees of cohesion such as may be required for different end-uses can be obtained by altering the temperature, or the amount of concentration of the solvent applied, or the solvent used. The temperature to which it is necessary to heat the wetted multifilament yarn in order to obtain cohesion depends on the degree of orientation or crystallinty of the yarn; thus a poly(ethylene terephthalate) yarn drawn over a snubbing pin at about C. has a lower degree of orientation and crystallinity than a yarn which has been drawn over the snubbing pin and then over a hot plate at C. The latter yarn usually requires to be heated at a temperature about 10 C. higher than the former to provide a similar degree of cohesion, under otherwise identical conditions and using the same solvent.

The cohered filament count as used in this specification is determined by cutting the cohered yarns whereby the coherence between the filaments is destroyed to an extent depending on the degree of coherence of the filaments in the yarn, that is to say a yarn of a low degree of cohesion and therefore a high filament count is more easily broken into single filaments, whereas bundles of filaments remain, on cutting a yarn having a high degree of cohesion. A suitable instrument is commercially available in the Mantra yarn filament counter developed by the British Rayon Research Association and made by Newmark Instruments Ltd. Its method and apparatusV is designed for counting the number of filaments in a multifilament yarn. The instrument is described in B P. 829,330 and in Man-Made Textiles of March 1958, pp. 38-39. For use of the commercially available instrument in counting the number of filaments in a multifilament yarn it is stated that the yarn must not have been sized or subjected to a finishing process which tends to cause the filaments to stick together or that if the yarns have a large amount of twist, it is advisable to remove most of the twist from the yarns before testing. For our purpose, however, it can be used to count the uncohered individual filaments or bundles of cohered filaments in a multifilament yarn. Clearly we are not concerned with the actual determination of the number of filaments in the yarn but with a measure of the number of filaments or groups of filaments which remain in an uncohered state at any point along the length of the yarn after cutting; the number of filaments indicated by the Manra counter, although not necessarily exactly the same as the number of filaments or groups of filaments indicated by other methods of measurement, provides a measure of the degree ofcohesion in the original sample of multifilament yarn. The number of filaments indicated by the Manra counter we have termed the cohered filament count or filament count. It will be appreciated that a low filament count signifies a high degree of cohesion, and vice versa. It will be appreciated that a number of measurements are required to give a statistically significant cohered filament count from a given length of yarn.

The Manra yarn filament counter uses a razor type cutter which cuts through a pretensioned filament yarn which is clamped between two clamps with the razor cutting between the clamps. Before cutting proceeds the distance between the clamps is gradually automatically increased by the movement of the clamps. The cutter of the instrument works through a dashpot mechanism allowing the cutter to bear steadily down on the yarn which is held under tension transverse to the cutter and the yarn is in contact with a sensing arm of a crystal transducer. As the yarn is cut the individual filaments or cohered filaments together separate from the rest of the yarn and there is a change in the force exe-rted on the sensing arm which produces a pulse which operates an electronic counter. The arrangement is such that the yarn is held under approximately the same tension for each test by having the yarn initially just taut in the yarn clamps and then moving the clamps apart by a finite amount. This operation and the bearing down of the cutter is done automatically when the switch operating the instrument is thrown.

We have determined that the tension applied to the yarn on the commercially available instrument is not critical and the differences in working tension which would be expected from instrument to instrument would not give a significantly different filament count.

A multifilament yarn having 24 filaments but which has not been treated according to our invention produces 23 or 24 pulses and the instrument registers a count of 23 or 24. When such a yarn, however, is treated with a solvent it is possible to obtain a filament count of between 2-24 compared with the theoretical possible count of 1-24.

Below the defined cohered filament count of no further benefit is obtained and the multifilament structure approaches the stiffness of a monofilament of corresponding denier and the structure is too rigid.

For use as a sewing thread where a high cohesion is required the cohered filament count should be in the region of 5-60% 0f the number of filaments in the unt-reated yarn.

Above 60% of the cohered filament count cohesion becomes insufficient to prevent filamen'tation taking place on guides of a sewing machine.

Thus a yarn containing 24 filaments should give a cohered filament count of from 2 to 14.

A yarn containing 12 filaments should give a count of from 2 to 7.

A yarn containing 36 filaments should give a count of from 2 to 21.

A yarn containing 72 filaments would require a count of from 4 to 42.

For cohered yarns for weaving a different cohered filament count is required. The bond between the filaments should preferably be broken down after the fabric has been woven so as to increase the covering power of the fabric. However' for some fabrics where high covering power is not required the yarns can be left substantially in their cohered form.

For use in weaving a coheredy filament count of l0- preferably l0-70%, of the number-of filaments in the untreated yarn is particularly useful. If the cohered filament count is above 80%, for example, in a 24 filament yarn if the filament count is above 20, the weaving performance is affected unless the yarn is also sized.

The advantages of our cohered yarns in weaving are:

(l) The elimination of the need for twisting and for sizing of all but the most lightly cohered yarns. This aids yarn processing since the Warp can be made directly from production bobbins andv then set up 0n the loom for weaving without any intermediate sizing or twisting operation.

(2) The cohered yarns are delustred. This is caused by the solvents used for the cohering process and this can have definite advantages, for example when it is not possible or expedient to produce a sufficiently delustred yarn for use in a particular fabric construction.

3) A variety of novel and desirable fabric effects can be obtained by a suitable combination of the cohered yarns with other yarns or with yarns having a different deg-ree of coherence and therefore a different appearance in fabric form; thus a lawn-like structure can be obtained by using a combination of cohered warp and fiat weft yarn or by using a warp with a higher degree ofvcohesion than in the weft. Alternatively a fabric can be woven with a combination of 2 or more yarns of different degrees of cohesion which can be treated in such a way so that the yarns having a low degree of cohesion can be broken down into individual filaments. The techniques suitable for separating the filaments in a cohered yarn include scouring, pressing, calendering, treatment with swelling agents or treatment in strongly alkaline solutions for example in sodium hydroxide.

(4) Further novel effects in fabric form can be obtained by weaving or knitting fabrics from yarns having a random filament bond. Partial break down of the filament cohesion causes various degrees of filamentation which tend to vary throughout the length of the yarn depending on the strength of the bond. This produces a desirable irregular yarn structure which becomes noticeable in the fabric.

Our yarns have particular merit for use in sewing threads because, I

(1) The twisting stage can be eliminated.

(2) The yarns can be processed more easily.

(3) Further bonding of the yarns to stop individual filaments from breaking from the yarn and to stop snarling of the broken filaments can be eliminated or the usual bonding treatment can be modified.

Cohesion of the filaments is preferably carried out by the synthetic filament yarn manufacturer and may be carried out before, during or after drawing. Since it is necessary to provide heat to cohere the yarn and to remove surplus solvent by evaporation lwe provide a process in which this heating is integrated with an existing heating process necessary during the manufacture of the yarn thus:

(1) The solvent may be applied to an undrawn yarn immediately before drawing. The yarn is then drawn using heat and the yarn is cohered during heat setting.

(2) The solvent may be applied to drawn yarn which has not been heat set and the yarn is subsequentlyk cohered during the heat setting stage as in (1) above.

(3) The solvent may be applied to drawn, heat set yarn and the required degree of cohesion-may Abeobtained in a separate heating step, and before windup, which is preferred.

' If the best yarn physical properties are desired i.e'. highest tenacity, then itis desirable that its solvent should be applied to the yarn after heat setting. However-if high yarn tenacities are not essential and if in any drawing process it is not convenient to apply solvent after heat setting; then application immediately prior to drawing or heat setting may be useful.

Suitable means for heating include hot air or vapour, contact with a hot plate or a heated roller, or radiant heating including infra-red and high frequency heating.

The lament Vcount obtained by cohering a given sample of yarn may be adjusted (a) By selecting a particular solvent (b) By adjusting the amount of solvent applied to 1-70% by weight of the yarn. This may be done by adjusting the pressure on nip rolls which express excess solvent from the yarn or by metering the quantity of solvent applied.

(c) By adjusting the temperature and duration of the heat treatment or the volume of air being circulated in the case of heating in or with hot air.

It is desirable that the multifilament yarn should be maintained under controlled tension during the heating stage. It is however an advantage of the process that the properties of the cohered yarn may he modified according tothe amount of tension applied. If the tension is controlled at a relatively low level slight shrinkage occurs whereas if the tension is controlled at a relatively high level slight stretching occurs; in the latter case a substantial increase in tenacity can -be obtained.

An important feature of the process of this invention is that little or no distortion of the shape of individual filaments or ofthe multifilament yarn need occur during the process; i.e. the force applied to hold the individual filaments together is insufiicient to cause distortion. However it is possible, if desired, to apply additional forces during the heating process in order to distort the shape of the resulting cohered multifilamentor of the individual yarns and thus to obtain, for example, ribbon-like structures.

Suitable solvents may have a boiling point either below or above'the temperature of treatment. The former are readily removed from the yarn by evaporation, and it is frequently desirable to use them in undiluted form. Solvents, particularly those which have a boiling point above the temperature of treatment, may `be retained in the yarn to a small extent even though completely evaporated from the surface, and this may result in slight plasticisation of the yarn land particularly of the bonds between filaments. Thiscan result in gradual changes in the strength of the bonds during the passage of time, such that. it becomes easier to separate individual filaments from each other, and can be an advantage where it is desirable to separate the Ifilaments in the finished product, in other Words -when a temporary bonding is required.

In the case of polyesterfilaments derived from terephthalic acid, such as poly(ethylene terephthalic), we have found that suitable solvents include tetrachloroethane, chloral, fy-butyrolactone, anisaldehyde, m-cresol, ben'z'ophenone and Z-phenoxyethanol, benzyl alcohol, acetophenone, salicylaldehyde, methyl cyclohexanone, acetophenone and a mixture of nitrowith chlorobenzene.

yIn the. case of filaments of polypropylene suitable solventsl include xylenes and a number of other known solvents for polypropylene.

It will be appreciated that the temperature required to cause inter-filament cohesion depends on the polymer from which the filaments are made and on the solvent used to produce cohesion.

If desired, the multifilament yarn may be brought into a particular configuration before, during vor after the application of the liquid containing the solvent. This may be done, for example, by passing the filaments through a tube in a high |velocity air stream and thereby generating an electric charge and causing inter-mingling and interlacing of the filaments, or by applying twist or false twist to the multifilament yarn or by using a crimped yarn, eg. twist crimped yarn.

It Iwill be appreciated that there are a number of interconnected `variables which require selection for successful operation and -we have found the following conditions suitable for poly(ethylene terephthalate) yarns (-a) Heat transfer from a solid metal surface: Temp. l40400 C.; range in degree seconds: 3-200.

(b) Heat transfer from a gas or vapour: Temp. 280- 600 C.; range in degree-seconds: Y().5-200.

(c) Amount of solvent: l l80% on weight of yarn, preferred: 2-3()% on weight of yarn (d) Drawn yarn total denier l5-l,000 (e) Total number of filaments in uncohered state: 5-200.

Belo-w the minimum conditions of time, temperature and deg./sec,-no useful cohesion is obtained. V

Above the maximum conditions, the yarn properties are impaired and even total breakdown of the yarn threadline may occur.

Below the minimum solvent quantity no useful cohesion is obtained, above the maximum amount it becomes difficult to remove excess and the quantity consumed makes the process commercially unattractive.

The bond between any two filaments consists solely of the polymer of which the filaments are composed in a crystalline or partly crystalline form. This crystallinity may be detected by examining the material of which the bond is composed -by X-rays, -when it is found to give an X-ray pattern typical of the polymer in a crystalline form. The material of which the bond is composed is not, in general, as highly oriented as the material within the filaments, but may exhibit some degree of orientation. Chemically the material of which the bond is composed is the same as the polymer from which the filaments have been made and the material forms therefore a chemically continuous phase.

The attached drawings illustrate particular embodi- -ments of our invention in which FIGURE l is a diagrammatic view of a longitudinal section of a cohered multifilament yarn on a greatly enlarged scale.

FIGURE 2 is a view of a yarn as in FIGURE 1 when some of the bonds between the filaments have been partly broken down.

FIGURE 3 is a diagrammatic vie-w of a yarn being cut on a filament yarn counter.

FIGURE 4 is an enlarged view of the cutter of FIG- URE 3.

FIGURE 5 is a diagrammatic view of the apparatus for drawing and applying solvent to the yarn.

Referring to FIGURE l a number of cohered filaments 1, 1a, 1b, 1c, fld, 1e, 1f are shown in longitudinal section and it will be noticed that there is a gap of an uncohered portion 2 between filaments 1c and 1d. When the cohered yarn is subjected to an after treatment such as calendering in fabric form or treatment with caustic sodium hydroxide, partial separation of the cohered filaments occurs to form gaps 3, 4, 5, 6 and 7 between the filaments, as shown in FIGURE 2.

FIGURE 3 shows diagrammatically the testing of a cohered yarn 8 as it is being cut by a cutter 9 whilst being clamped between' clamps 10 and 11 which are moved farther apart before cutting to provide tension so that the uncohered filaments separate on cutting into individual fibre ends shown at 12. A sensing arm 13 of a crystal transducer is in contact with the pretensioned yarn as it is being cut and pulses which are produced by cutting the yarn operate an electronic counter (not shown).

FIGURE 4 is an enlarged view of the cutter 9 shown in FIGURE 3 and shows separation of small bundles of filaments 14 and 15 as the yarn is being cut.

FIGURE shows an undrawn yarn at 8a being drawn between feed roll 16 with associated idler roll 17 and draw roll 18 With associated idler roll 19. After looping the yarn four turns on the feed and draw roll it is passed over a spaced idler roll 20 back to the draw roll 18 with associated idler roll 19. Bet-Ween the idler roll 20 and the draw roll is a driven solvent applicator roll 21 rotating in a trough of solvent 22. The yarn bearing the solvent. after making another set yof four turns over the draw roll, where cohesion and drying occurs, is passed through a cooling zone before being wound up.

The following examples illustrate but do not limit our invention.

EXAMPLE 1 A 52 denier 24 filament delustred poly(ethylene terephthalate) multilament yarn of tenacity 5.1 g.p.d. and extensibility 35% was passed through a bath of tetrachloroethane then round a feed roll, over a hot plate and round a draw roll, `at 100 ft./min. and was finally wound up on .a bobbin. 'I he yarns obtained at different hot-plate temperatures were tested by extension to break on an Instron testing machine. Yarns treated at 160-200 C. were completely cohered, so that they ybroke as a single unit (giving a cohered filament count of 3-4); yarns treated at 14S-150 C. broke in up to 10 steps, and gave a filament count of -14 on the Maura counter; yarns treated at 137-142 C. broke in ten to twenty steps and gave a cohered filament yarn count of -19; yarns treated below 135 C. 4and untreated yarns broke as individual filaments in about twenty-four steps, giving a lilament count of 23-24.

EXAMPLE 2 A poly(ethylene terephthalate) multifilament yarn of denier 125.7, containing 24 filaments, was treated as in Example 1 with the hot plate at 180 C. When the yarn was allowed to run under only slight tension shrinkage occurred and the final denier was 129.7; there was a decrease in tenacity from 6.7 g.p.d. to 6.4 g.p.d., .and an increase in extensibility from 15% to 23.%. When the yarn was caused to mn under high tension stretching occurred and the final denier was 113.9; there was an increase in tenacity from 6.7 g.p.d. to 80 g.p.d., and a decrease in extensibility from 15% to 9%. On the Instron tester a single break was recorded. The yarns when tested with the Maura counter gave a cohered filament count of 2-5.

EXAMPLE 3 A number of solvents were tested with yarns of Example 1 and Example 2 at a plate temperature of 180 C. Cohesion to a filament count of 3-15 was obtained with ly-butyrolactone, methyl cyclohexanone, acetophenone, salicylaldehyde, benzyl alcohol, methyl salicylate, nitrobenzene, a 1:1 mixture by volume of nitro benzene and chlorobenzene, and an aqueous emulsion of tetrachloroethane, but not with chlorobenzene, anisole, dimethyl forma'mide, ethylene glycol, ethylene diacetate, dimethyl maleate, bromobenzene, or o-dichlorobenzene. Cohesion was obtained with o-dichlorobenzene, however, when the plate temperature was raised to 205 C. or above.

EXAMPLE 4 A 50 denier tow composed of 24 drawn and oriented filament of polyethylene terephthalate was wetted with 25% of its weight of benzyl alcohol and passed over a 12" hot plate maintained at 270-275 C. at a yarn speed of 1500 ft./min. and under a tension of g. The yarn was then wound onto a package. A full arc of contact was maintained on -the hot plate. The resulting cohered yarn had a filament count of 15.

It will 4be appreciated that the degree of cohesion may be adjusted within the defined limit of 5-80% and that it increases with:

(i) Increasing hot plate temperature (ii) Decreasing yarn speed.

(iii) Decreasing tow denier (iv) Increasing amount of solvent applied, providing that the amount is' not sufficient seriously to affect the temperature attained by the yarn in passage over the hot plate.

EXAMPLE 5 In order to demonstrate that the cohering process can be readily coupled -with the drawing stage an undrawn tow of polyethylene terephthalate was drawn on a conventional filament yarn drawframe and heat set on a hot plate. 25%, by weight of the yarn, of benzyl alcohol was applied immediately after the heat" setting zone and the yarn passed over an additional hot plate maintained at the temperature required to cohere the yarn as in Example 4. The resulting cohered yarn had a filament count of 15.

EXAMPLE 6 Benzyl alcohol, 35% by weight of fibre, was applied to a 50 denier tow consisting of 24 filament of drawn and oriented polyethylene terephthalate.v The wet tow was passed down a tube 17 long and approximately 1'1/2" diameter, through which hot air at a temperature of S30- 35 0 C. was circulated at a rate `of 1 to 2 litres/min. The wind-up speed was maintained at 500 ft./min. to give a cohered yarn having a filament count of 3.

EXAMPLE 7 A A 160 denier tow comprised of 24 undrawn land oriented filaments of polyethylene terephthalate was drawn on a system comprising two heated rolls of the same diameter of 41/2, the feed roll, maintained at 90 C. and rotating at approximately 1/3 of the speed of the second, the draw roll, which was maintained at 180 C. Each roll had an associated separator roll so that the yarn could make more than one complete turn round the heated rolls, and in this case four turns were taken round each roll. The drawn yarn, after leaving the hot draw roll, now of about 50 denier, was taken round a further separator roll situated some 2 ft. from the draw roll and 25%, by weight of the fibre, of benzyl alcohol was applied to the yarn. The wet yarn was then fed back to the draw roll and four complete turns were taken round the roll. The cohered yarn was wound onto a package at 1,000 ft./min. The filament count was 6.

EXAMPLE 8 A tow comprised of 48 undrawn and oriented filaments of polyethylene terephthalate of total denier 1090 was drawn between two rolls of the same diameter but revolving at different speeds such that a draw ratio of 4.38 was applied. In addition the rolls were heated, the slower roll to a surface temperature of C. and the faster draw roll to a temperature of C. The drawn yarn was taken from the draw roll over a free running separator roll after which 35%, by weight of libre, of benzyl alcohol was applied and the yarn was passed through a lagged metal tube 16 long and 1/s" internal diameter, into the centre of which steam at 450 C. was passed. The yarn was wound on to a package at 400 ft./min. The yarn had a cohered yfilament count of 14.

EXAMPLE 9 A tow consisting of 24 undrawn filaments of poly(ethyl ene terephthalate) of total denier 545 was treated as in Example 7, except that the draw ratio was 4.38, the faster draw roll was operated at a temperature of 215 C., a 50% emulsion of benzyl alcohol in water was applied to -give 7% of benzyl alcohol on the drawn yarn, and the wetted yarn was taken eight times round the draw roll before cooling and winding up at 700 feet per minute. The filament count was 4.

EXAMPLE 10 A tow consisting of 24 undrawn filaments of poly (ethylene terephthalate) of total denier 161 was treated as in Example 9, except that the faster draw roll was operated at a temperature of 190 C., and the amount of benzyl alcohol applied t the fibre was 4% (equal t0 8% of a 50% emulsion in water). The filament count was 6.

EXAMPLE 1 1 A tow consisting of 24 undrawn filaments of poly(eth ylene terephthalate) of total denier 545 was treated as in Example 9, except that only 2% of benzyl alc-0h01 Was applied (4% of a 50% emulsion). The filament count was l5.

EXAMPLE 12 To illustrate the influence of temperature Example 4 is repeated except that: the temperature of the hot plate is maintained at 278-285 C., the yarn has a cohered filament count of 8-12.

EXAMPLE 13 Example 4 is repeated except that the temperature of the hot plate is maintained at 287-295 C. A yarn of cohered filament count 4-6 is obtained.

EXAMPLE 14 To illustrate the influence of yarn speed Example 4 is repeated except that the yarn speed is decreased to 1200 ft./min. A yarn of cohered filament count `7-9 is obtained.

EXAMPLE 15 To illustrate the influence of solvent pickup Example 4 is repeated except that the solvent level is increased to 30%. A yarn of filament count 10-12 is obtained. For comparison if the solvent level is decreased to 15% a yarn of filament count is obtained.

COMPARATIVE EXAMPLE 16 To illustrate the infiuence of tow denier, Example 4 is repeated except that the tow denier is increased to 125. The yarn in this comparative example is uncohered and has a filament count of 24, and a yarn of 75 denier gives a filament count of approximately 20.

EXAMPLE 17 10 bricant is a silicone iiuid having a viscosity at 25 C. between 1,000 and 10,000 centistokes, which is conveniently applied as an emulsion in water, using e.g. 35% of the silicone fluid. Polydimethyl siloxane is the preferred silicone fluid having a viscosity at 25 C. of 5,000 centistokes.

What we claim is:

1. A coherent thermoplastic substantially twistless multifilament yarn of denier less than about 1090 made from polyethylene terephthalate possessing in the form of oriented fibres a water absorbency of less than 1% at F, and 65% relative humidity, wherein each filament adheres to adjacent filaments by bonds extending substantially for the Whole length of the filaments, each bond varying in strength along its length, said bond consisting of the polyethylene terephthalate of which the filaments are composed so that any cohered portion between and including the filaments consists of a chemically continuous phase of the same polymer further characterised in that said bond consists of the polymer in a crystalline or partly crystalline form, the degree of cohesion being defined by an average cohered filament count of about 8- of the total number of filaments in'the untreated and uncohered yarn.

2. A coherent multifilament yarn according to claim 1 for use as a sewing thread in which the cohered filament count is 5 to 60% of the number of filaments in the untreated and uncohered yarn.

3. A coherent multifilament yarn according to claim 1 for use in weaving in which the cohered filament count is 10 to 70% of the number of filaments in the untreated and uncohered yarn.

4. A fabric comprising coherent multifilament yarns according to claim 1, yarns having a different degree of coherence being combined in said fabric.

5. A woven fabric comprising coherent multifilament yarns according to claim 1, the filaments in the warp of said fabric being of a higher degree of cohesion than the filaments in the weft.

References Cited UNITED STATES PATENTS 3,117,906 1/1964 Tanner 161-177 3,161,706 12/1964 Peters 161--177 3,164,947 l/1965 Gaston 161-177 3,151,011 9/1964 Troelman et al. 156-180 JACOB H. STEINBERG, Primary Examiner. 

1. A COHERENT THERMOPLASTIC SUBSTANTIALLY TWISTLESS MULTIFILAMENT YARN OF DENIER LESS THAN ABOUT 1090 MADE FROM POLYETHYLENE TEREPHTHALATE POSSESSING IN THE FORM OF ORIENTED FIBRES A WATER ABSORBENCY OF LESS THAN 1% AT 70*F. AND 65% RELATIVE HUMIDITY, WHEREIN EACH FILAMENT ADHERES TO ADJACENT FILAMENTS BY BONDS EXTENDING SUBSTANTIALLY FOR THE WHOLE LENGTH OF THE FILAMENTS, EACH BOND VARYING IN STRENGTH ALONG ITS LENGTH, SAID BOND CONSISTING OF THE POLYETHYLENE TEREPHTHALATE OF WHICH THE FILAMENTS 